• Transactions on Electrical and Electronic Materials
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• 제7권4호
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• pp.189-195
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• 2006

The microstructure, electrical and dielectric properties, and stability against DC accelerated aging stress of the varistors, which are composed of quaternary system $ZnO-Pr_6O_{11}CoO-Cr_2O_3-based$ ceramics, were investigated for different $La_2O_3$ contents. The increase of $La_2O_3$ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0mol%. The highest nonlinearity was obtained from 0.5mol% $La_2O_3$, with the nonlinear coefficient of 81.6 and the leakage current of $0.1{\mu}A$. The varistors doped with 0.5mol% $La_2O_3$ exhibited high stability, in which the variation rates of breakdown voltage, nonlinear coefficient, leakage current, dielectric constant, and dissipation factor were -1.1%, -3.7%, +100%, +1.4%, and +8.2%, respectively, for stressing state of $0.95V_{1mA}/150^{\circ}C/24h$.

• 한국세라믹학회지
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• 제38권8호
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• pp.693-697
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• 2001

고상반응법으로 이론 밀도의 약 92%의 소결 밀도를 갖는 입방정계의 새로운 이온전도체 L $a_{2-x}$S $r_{x}$M $o_{2-y}$C $r_{y}$ $O_{9-{\delta}}$(x=0, 0.05, y=0, 0.1)를 제조하였다. 교류 복소임피던스는 3$50^{\circ}C$~90$0^{\circ}C$의 온도범위에서 공기중에서 측정하여, EQUIVCRT 모델링 소프트웨어로 해석하였다. 상 전이온도인 58$0^{\circ}C$ 전.후로 임피던스 스펙트럼에 큰 차이가 있었으며, 전기전도도는 L $a_2$M $o_2$ $O_{9}$ 시편의 경우 7$50^{\circ}C$에서 3$\times$$10^{-2}$ S$cm^{-1}$ /로 우수하였으며, 활성화 에너지는 고온 상 영역에서는 0.89 eV, 저온 상 영역에서는 1.12 eV이었다. 순수한 L $a_2$M $o_2$ $O_{9}$과 비교하여 Cr 치환효과는 크지 않았으나, Sr 치환 시에는 상 전이온도의 감소와 전기전도도의 증가 현상을 보였으며, 전이온도 부근에서의 전기전도도 변화 폭은 작았다.다.

• 대한의용생체공학회:의공학회지
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• 제16권3호
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• pp.331-336
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• 1995

체내 매입후 경시적으로 분해되면서 재생골조직에 의해 치환되는 인공골복합체를 제조하고 복합체가 세포활성에 미치는 영향을 조사하였다. 복합체시편을 세포배양액에 넣고 1주일동안 $37^{\circ}C$에서 배양한 다음, 사람자궁경부암유래 HeLa S3세포와 쥐피하 L929세포를 복합체가 용해된 세포배양액에서 5일간 배양하여 세포성장율을 비교하여 세포특성을 조사하였다. 한편 HeLa S3세포를 배양중인 배양액에 ${Na_2}^{51}CrO_4$를 첨가하여 HeLa S3세포에 $^{51}Cr$를 표식한 다음, 용해된 $^{51}Cr$의 양을 $\gamma$-counter를 이용하여 측정하였다. 세포성장정도의 측정에서는 HeLa S3 세포 및 L929 세포 모두가 특이한 세포독성을 발견할 수 없었으며, 복합체가 용해된 세포배양액내의 표식된 HeLa S3 세포로 부터 용해된 $^{51}Cr$량을 측정한 결과, 세포활성을 저해하지 않은 것으로 관찰되었다.

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2002년도 추계총회 및 연구발표회 초록집
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• pp.121.1-121
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• 2002

• 한국분말재료학회지
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• 제16권3호
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• pp.185-190
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• 2009

Fe-Cr steels are the most promising candidate for interconnect in solid oxide fuel cells. In this study, an effective, dense and well adherent (LaSr)(CrCo)$O_3$ [LSCC] coating layer was produced onto 430 stainless steel (STS-430) by atmospheric plasma spraying and the oxidation behavior as well as electrical properties of the LSCC coated STS-430 were investigated. A significant oxidation of pristine STS-430 occurred at $800^{\circ}C$ in air environment, leading to the formation of $Cr_2O_3$ and $FeCr_2O_4$ scale layer up to ${\sim}7{\mu}m$ after 1200h, and consequently increased an area specific resistance of $330\;m{\Omega}{\cdot}cm^2$. Although the plasma sprayed LSCC coating contained the characteristic pore network, the coated samples presented apparent advantages in reducing oxidation growth of STS-430, resulting a decrease in oxide scale thickness of ${\sim}1{\mu}m$ at $800^{\circ}C$ after 1200h. The area specific resistance of the LSCC coated STS-430 was much reduced to ${\sim}7\;m{\Omega}{\cdot}cm^2$ after exposure at $800^{\circ}C$ for 1200h, compared to that of the pristine STS-403.

• 한국세라믹학회지
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• 제49권2호
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• pp.197-203
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• 2012

In this study, in order to improve densification of $La_{0.8}Ca_{0.2}Cr_{0.9}Co_{0.1}O_{3-\delta}$ (LCCC), which is known for one of the most proper candidate interconnector materials in the solid oxide fuel cells, $CaCrO_4$ was prepared via solid oxide synthesis route and added to the LCCC with different amount and particle sizes. As the amount of the $CaCrO_4$ increased, porosity of the sintered samples increased, and the pore size was proportional to the particle size of the $CaCrO_4$. This supports the fact that the $CaCrO_4$ phase forms liquid during sintering and permeate into the matrix leaving behind large pores. Then the liquid reacts with the matrix through the solid solution. However, when the samples were sintered with a slow ramp up rates, the porosity decreased. This is thought to be caused by the progressive solid solution of $CaCrO_4$ before the temperature reach to the melting temperature and forms a fluent amount of liquids. The sintering behavior of the LCCC with the addition of $CaCrO_4$ was analyzed through the transient liquid phase sintering on the basis of the microstructure observation and phase identification by x-ray diffraction.

• 한국세라믹학회지
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• 제43권6호
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• pp.383-388
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• 2006

The varistor properties and DC accelerated aging characteristics of $ZnO-Pr_{6}O_{11}-CoO-Cr_{2}O_{3}$-based varistors were investigated at different $La_{2}O_3$ contents in the range of $0{\sim}2.0mol%$. The varistors doped with 0.5 mol% $La_{2}O_3$ exhibited good nonlinearity, with 81.6 in nonlinear coefficient. Increasing the $La_{2}O_3$ content further to 2.0 mol% caused the sintered density to increase, and the breakdown voltage and nonlinearity to decrease abruptly. The varistors with 0.5 mol% $La_{2}O_3$ exhibited the high electrical stability, with -1.14% in variation rate of breakdown voltage, -3.7% in variation rate of nonlinear coefficient, and +100% in variation rate of leakage current for specified DC accelerated aging stress condition (95% of breakdown voltage/$150^{\circ}C$/24 h).

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.39-44
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• 2011

Sub-micrometer $La_{0.8}Ca_{0.2}CrO_3$ powders for ceramic interconnects of solid oxide fuel cells were synthesized by the aqueous combustion process. The materials were prepared from the precursor solutions with different glycine (fuel)-to-nitrate (oxidant) ratios (${\phi}$). Single-phase $La_{0.8}Ca_{0.2}CrO_3$ powders with a perovskite structure were obtained after combustion when ${\phi}$ was equal to or larger than 0.480. Especially, the stoichiometric precursor with ${\phi}$ = 0.555 yielded the spherical $La_{0.8}Ca_{0.2}CrO_3$ particles with 150-250 nm diameters after calcination at $1000^{\circ}C$. When compared with the powders synthesized by the solid-state reaction, the combustion-derived, fine powders exhibited improved sinterability, leading to near-full densification at $1400^{\circ}C$ in oxidizing atmospheres. Moreover, a small quantity of glass additives was used to reduce the sintering temperature, and considerable densification was indeed achieved at temperatures as low as $1100^{\circ}C$.

• 한국안전학회지
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• 제3권1호
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• pp.7-13
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• 1988

The oxides in perovskite type, $LaMO_3$ (M=Ni, Cr, Fe, Co), compared with gas sensors which have been used, were synthesised and then examined sensor response comparatively in order to make a thick film gas sensor having a good gas selectivity, durability and simple manufacturing. The oxides in perovskite type, $LaFe_{1-x}O_3$ (x=0.2, 0.4, 0.6, 0.8), which a part of Fe was replaced with Co, were examined with regard to their electric resistance with variable temperature and sensor response for carbon monoxide gas.

• 대한환경공학회지
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• 제28권4호
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• pp.368-375
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• 2006

순수한 아나타제 구조로 이루어진 DT51D $TiO_2$에 $CrO_x,\;FeO_x,\;MnO_x,\;LaO_x,\;CoO_x,\;NiO_x,\;CeO_x,\;CuO_x$와 같은 단일 산화물 촉매를 각각 5 wt.% 담지하여 모델반응으로 선택한 기상 TCE 제거반응을 수행하였으며, 이로부터 얻어진 결과를 바탕으로 $CrO_x/TiO_2$-based 복합 산화물 촉매상에서 TCE 산화반응을 연구함으로써 유해 중금속의 사용량을 최소화하기 위한 최적의 촉매 디자인 방법을 도출하고자 하였다. DT51D $TiO_2$에 담지된 여러 단일 금속 산화물들 중에서 기상 TCE 제거반응에 대하여 $CrO_x$가 가장 우수한 촉매활성을 보이는 것으로 나타났으며, 반응온도의 함수로 얻어진 TCE 제거반응의 활성은 $CrO_x$의 담지량에 의존하였다. 5 wt.% $CrO_x$-based 복합 산화물 촉매는 10 wt.% $CrO_x$만으로 이루어진 단일 산화물 촉매와 거의 동일한 수준의 TCE 제거반응 활성을 보였을 뿐만 아니라 이 복합 산화물 촉매들은 10 wt.% $CoO_x,\;MnO_x,\;FeO_x,\;NiO_x$ 등과 같은 단일 산화물 촉매들보다 높은 반응활성을 갖는 것으로 나타났다. 단일 산화물 촉매의 반응활성과 비교하였을 때 5 wt.% $CrO_x$-based 복합 산화물 촉매상에서 TCE 제거반응 동안에 얻어지는 반응활성의 증가 정도는 $420^{\circ}C$ 이하의 반응온도 기준으로 약 $10{\sim}80%$ 이상이었다. 따라서, CVOCs 제거반응을 위하여 널리 사용되고 있는 단일 $CrO_x/Al_2O_3$ 촉매보다는 $CrO_x$의 사용량을 최소화하면서도 우수한 반응활성을 얻을 수 있는 $CrO_x/TiO_2$-based복합 산화물 촉매가 보다 바람직하며 하나의 대안적인 촉매 디자인 방법으로 응용될 수 있을 것으로 생각된다.